Strong long-range perpendicular exchange bias across a spacer layer

Chunjiao Pan,Yoshio Nakamura,Ji Shi,Zhengjun Zhang,Takashi Harumoto,Hongyu An

doi:10.1063/1.5128308

Abstract

The perpendicular magnetic anisotropy (PMA) and perpendicular exchange bias (PEB) have been investigated in a CoPt/spacer/FeMn heterostructure by inserting Ta and Pt as spacer layers, respectively. First, we show that strong PMA can be obtained in (111)-oriented A1-CoPt single layer and CoPt/FeMn bilayer films on MgO (111) substrates. Then we demonstrate that the Ta and Pt spacer layers have largely different effects on the PMA and PEB of the CoPt/spacer/FeMn films. By increasing the thickness of the Ta spacer layer to 1 nm, the PMA and PEB drastically decrease. While, in the case of Pt, the PMA and PEB increase first, then slightly decrease. When the Pt spacer layer is 1 nm, a value of 85 Oe of the long-range PEB still can be obtained. The possible mechanisms were discussed to explain the different trends of PMA and PEB. Since Ta and Pt are the generally used materials in the spintronics, our study provides a piece of information for the control of the magnetic anisotropy and exchange bias in the current-induced magnetization switching of ferromagnet without external magnetic field.

Highlights

The epitaxial strain between CoPt and MgO
We study the perpendicular magnetic anisotropy (PMA) and perpendicular exchange bias (PEB) in a CoPt/spacer/ FeMn heterostructure by inserting Ta and Pt spacer layers, respectively
We demonstrate that the Ta and Pt spacer layers have different effects on the PMA and PEB in the CoPt/spacer/FeMn films

Summary

Introduction

The epitaxial strain between CoPt and MgO. Since the about 10% mismatch of the lattice constant between A1- CoPt (0.38 nm) and MgO (0.42 nm) results in a tensile stress in the CoPt layer, which favors PMA.[24,25] The field cooling (FC) treatment was conducted by cooling down the CoPt/FeMn bilayer film from 230 ○C to room temperature. Thomas et al.[16] reported that by inserting Al, Ag, Au, Si, Pd, Ru and Ti as spacer layers in the Fe16Co16/spacer/Ir22Mn78 films, the EB decreases exponentially in most cases by increasing the thickness of the spacer layers. We study the perpendicular magnetic anisotropy (PMA) and perpendicular exchange bias (PEB) in a CoPt/spacer/ FeMn heterostructure by inserting Ta and Pt spacer layers, respectively.

Results

Conclusion